The phenomenon we call tsunami is a series of large waves of extremely long wavelength and period usually generated by a violent, impulsive undersea disturbance or activity near the coast or in the ocean. When a sudden displacement of a large volume of water occurs, or if the sea floor is suddenly raised or dropped by an earthquake, big tsunami waves can be formed by forces of gravity. The waves travel out of the area of origin and can be extremely dangerous and damaging when they reach the shore. The word tsunami (pronounced tsoo-nah'-mee) is composed of the Japanese words "tsu" (which means harbor) and "nami" (which means "wave"). Often the term, "seismic or tidal sea wave" is used to describe the same phenomenon, however the terms are misleading, because tsunami waves can be generated by other, non seismic disturbances such as volcanic eruptions or underwater landslides, and have physical characteristics different of tidal waves. The tsunami waves are completely unrelated to the astronomical tides  which are caused by the extraterrestrial, gravitational influences of the moon, sun, and the planets. Thus, the Japanese word "tsunami", meaning "harbor wave" is the correct, official and all-inclusive term. It has been internationally adopted because it covers all forms of impulsive wave generation.Back to Top

2. How do earthquakes generate tsunamis?

By far, the most destructive tsunamis are generated from large, shallow earthquakes with an epicenter or fault line near or on the ocean floor. These usually occur in regions of the earth characterized by tectonic subduction along tectonic plate boundaries. The high seismicity of such regions is caused by the collision of tectonic plates. When these plates move past each other, they cause large earthquakes, which tilt, offset, or displace large areas of the ocean floor from a few kilometers to as much as a 1,000 km or more. The sudden vertical displacements over such large areas, disturb the ocean's surface, displace water, and generate destructive tsunami waves. The waves can travel great distances from the source region, spreading destruction along their path. For example, the Great 1960 Chilean tsunami was generated by a magnitude 8.3 earthquake that had a rupture zone of over 1,000 km. Its waves were destructive not only in Chile, but also as far away as Hawaii, Japan and elsewhere in the Pacific. It should be noted that not all earthquakes generate tsunamis. Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami.Back to Top

3. How do volcanic eruptions generate tsunamis?

Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area. According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse/engulfment of the volcanic magmatic chambers. One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people. It is also believed that the destruction of the Minoan civilization in Greece was caused in 1490 B.C. by the explosion/collapse of the volcano of Santorin in the Aegean Sea.Back to Top

Less frequently, tsunami waves can be generated from displacements of water resulting from rock falls, icefalls and sudden submarine landslides or slumps. Such events may be caused impulsively from the instability and sudden failure of submarine slopes, which are sometimes triggered by the ground motions of a strong earthquake. For example in the 1980's, earth moving and construction work of an airport runway along the coast of Southern France, triggered an underwater landslide, which generated destructive tsunami waves in the harbor of Thebes. Major earthquakes are suspected to cause many underwater landslides, which may contribute significantly to tsunami generation. For example, many scientists believe that the 1998 tsunami, which killed thousands of people and destroyed coastal villages along the northern coast of Papua-New Guinea, was generated by a large underwater slump of sediments, triggered by an earthquake.

In general, the energy of tsunami waves generated from landslides or rock falls is rapidly dissipated as they travel away from the source and across the ocean, or within an enclosed or semi-enclosed body of water  such as a lake or a fjord. However, it should be noted, that the largest tsunami wave ever observed anywhere in the world was caused by a rock fall in Lituya Bay, Alaska on July 9, 1958. Triggered by an earthquake along the Fairweather fault, an approximately 40 million cubic meter rock fall at the head of the bay generated a wave, which reached the incredible height of 520-meter wave (1,720 feet) on the opposite side of the inlet. A initial huge solitary wave of about 180 meters (600 feet) raced at about 160 kilometers per hour (100 mph) within the bay debarking trees along its path. However, the tsunami's energy and height diminished rapidly away from the source area and, once in the open ocean, it was hardly recorded by tide gauge stations.Back to Top

5. Can asteroids, meteorites or man-made explosions cause tsunamis?

Fortunately, for mankind, it is indeed very rare for a meteorite or an asteroid to reach the earth. No asteroid has fallen on the earth within recorded history. Most meteorites burn as they reach the earth's atmosphere. However, large meteorites have hit the earth's surface in the distant past. This is indicated by large craters, which have been found in different parts of the earth. Also, it is possible that an asteroid may have fallen on the earth in prehistoric times  the last one some 65 million years ago during the Cretaceous period. Since evidence of the fall of meteorites and asteroids on earth exists, we must conclude that they have fallen also in the oceans and seas of the earth, particularly since four fifths of our planet is covered by water.

The fall of meteorites or asteroids in the earth's oceans has the potential of generating tsunamis of cataclysmic proportions. Scientists studying this possibility have concluded that the impact of moderately large asteroid, 5-6 km in diameter, in the middle of the large ocean basin such as the Atlantic Ocean, would produce a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States. On both sides of the Atlantic, coastal cities would be washed out by such a tsunami. An asteroid 5-6 kilometers in diameter impacting between the Hawaiian Islands and the West Coast of North America, would produce a tsunami which would wash out the coastal cities on the West coasts of Canada, U.S. and Mexico and would cover most of the inhabited coastal areas of the Hawaiian islands. Conceivably tsunami waves can also be generated from very large nuclear explosions. However, no tsunami of any significance has ever resulted from the testing of nuclear weapons in the past. Furthermore, such testing is presently prohibited by international treaty.Back to Top

6. Where and how frequently are tsunamis generated?

Tsunamis are disasters that can be generated in all of the world's oceans, inland seas, and in any large body of water. Each region of the world appears to have its own cycle of frequency and pattern in generating tsunamis that range in size from small to the large and highly destructive events. Most tsunamis occur in the Pacific Ocean and its marginal seas. The reason is that the Pacific covers more than one-third of the earth's surface and is surrounded by a series of mountain chains, deep-ocean trenches and island arcs called the "ring of fire"  where most earthquakes occur (off the coasts of Kamchatka, Japan, the Kuril Islands, Alaska and South America). Many tsunamis have also been generated in the seas which border the Pacific Ocean.

Tsunamis are generated, by shallow earthquakes all around the Pacific, but those from earthquakes in the tropical Pacific tend to be modest in size. While such tsunamis in these areas may be devastating locally, their energy decays rapidly with distance. Usually, they are not destructive a few hundred kilometers away from their sources. That is not the case with tsunamis generated by great earthquakes in the North Pacific or along the Pacific coast of South America. On the average of about half-a-dozen times per century, a tsunami from one of these regions sweeps across the entire Pacific, is reflected from distant shores, and sets the entire ocean in motion for days. For example, the 1960 Chilean tsunami caused death and destruction throughout the Pacific. Hawaii, Samoa, and Easter Island all recorded runups exceeding 4 m; 61 people were killed in Hawaii. In Japan 200 people died. A similar tsunami in 1868 from northern Chile caused extensive damage in the Austral Islands, Hawaii, Samoa and New Zealand. Although not as frequent, destructive tsunamis have been also been generated in the Atlantic and the Indian Oceans, the Mediterranean Sea and even within smaller bodies of water, like the Sea of Marmara, in Turkey. In 1999, a large earthquake along the North Anatolian Fault zone, generated a local tsunami, which was particularly damaging in the Bay of Izmit. In the last decade alone, destructive tsunamis have occurred in Nicaragua (1992), Indonesia (1992, 1994, 1996), Japan (1993), Philippines (1994), Mexico (1995), Peru (1996, 2001), Papua-New Guinea (1998), Turkey (1999), and Vanuatu (1999).Back to Top

7. How does tsunami energy travel across the ocean and how far can tsunamis waves reach?

Once a tsunami has been generated, its energy is distributed throughout the water column, regardless of the ocean's depth. A tsunami is made up of a series of very long waves. The waves will travel outward on the surface of the ocean in all directions away from the source area, much like the ripples caused by throwing a rock into a pond. The wavelength of the tsunami waves and their period will depend on the generating mechanism and the dimensions of the source event. If the tsunami is generated from a large earthquake over a large area, its initial wavelength and period will be greater. If the tsunami is caused by a local landslide, both its initial wavelength and period will be shorter. The period of the tsunami waves may range from 5 to 90 minutes. The wave crests of a tsunami can be a thousand km long, and from a few to a hundred kilometers or more apart as they travel across the ocean. On the open ocean, the wavelength of a tsunami may be as much as two hundred kilometers, many times greater than the ocean depth, which is on the order of a few kilometers. In the deep ocean, the height of the tsunami from trough to crest may be only a few centimeters to a meter or more  again depending on the generating source.

Tsunami waves in the deep ocean can travel at high speeds for long periods of time for distances of thousands of kilometers and lose very little energy in the process. The deeper the water, the greater the speed of tsunami waves will be. For example, at the deepest ocean depths the tsunami wave speed will be as much as 800 km/hr, about the same as that of a jet aircraft. Since the average depth of the Pacific ocean is 4000 m (14,000 feet), tsunami wave speed will average about 200 m/s or over 700 km/hr (500 mph). At such high speeds, a tsunami generated in Aleutian Islands may reach Hawaii in less than four and a half hours. In 1960, great tsunami waves generated in Chile reached Japan, more than 16,800 km away in less than 24 hours, killing hundreds of people.Back to Top

8. Why aren't tsunamis seen at sea or from the air?

In the deep ocean, tsunami wave amplitude is usually less than 1 m (3.3 feet). The crests of tsunami waves may be more than a hundred kilometers or more away from each other. Therefore, passengers on boats at sea, far away from shore where the water is deep, will not feel nor see the tsunami waves as they pass by underneath at high speeds. The tsunami may be perceived as nothing more than a gentle rise and fall of the sea surface. The Great Sanriku tsunami, which struck Honshu, Japan, on June 15, 1896, was completely undetected by fishermen twenty miles out to sea. The deep-water height of this tsunami was only about 40 centimeters when it passed them and yet, when it arrived on the shore, it had transformed into huge waves that killed 28,000 people, destroyed the port of Sanriku and villages along 275 km of coastline. For the same reason of low amplitude and very long periods in the deep ocean, tsunami waves cannot be seen nor detected from the air. From the sky, tsunami waves cannot be distinguished from ordinary ocean waves.Back to Top

9. What are the factors of destruction from tsunamis?

There are three: inundation, wave impact on structures, and erosion. Strong, tsunami-induced currents lead to the erosion of foundations and the collapse of bridges and seawalls. Flotation and drag forces move houses and overturn railroad cars. Considerable damage is caused by the resultant floating debris, including boats and cars that become dangerous projectiles that may crash into buildings, break power lines, and may start fires. Fires from damaged ships in ports or from ruptured coastal oil storage tanks and refinery facilities, can cause damage greater than that inflicted directly by the tsunami. Of increasing concern is the potential effect of tsunami draw down, when receding waters uncover cooling water intakes of nuclear power plants.Back to Top

10. What determines how destructive a tsunami will be near the origin and at a distant shore?

Tsunamis arrive at a coastline as a series of successive crests (high water levels) and troughs (low water levels)  usually occurring 10 to 45 minutes apart. As they enter the shallow waters of coastlines, bays, or harbors, their speed decreases to about 50-60 km/hr. For example, in 15 m of water the speed of a tsunami will be only 45 km/hr. However 100 or more kilometers away, another tsunami wave travels in deep water towards the same shore at a much greater speed, and still behind it there is another wave, traveling at even greater speed. As the tsunami waves become compressed near the coast, the wavelength is shortened and the wave energy is directed upward  thus increasing their heights considerably. Just as with ordinary surf, the energy of the tsunami waves must be contained in a smaller volume of water, so the waves grow in height. Even though the wavelength shortens near the coast, a tsunami will typically have a wavelength in excess of ten kilometers when it comes ashore. Depending on the water depth and the coastal configuration, the waves may undergo extensive refraction  another process that may converge their energy to particular areas on the shore and thus increase the heights even more. Even if a tsunami wave may have been 1 meter of less in the deep ocean, it may grow into a huge 30-35 meter wave when it sweeps over the shore. Thus, tsunami waves may smash into the shore like a wall of water or move in as a fast moving flood or tide  carrying everything on their path. Either way, the waves become a significant threat to life and property. If the tsunami waves arrive at high tide, or if there are concurrent storm waves in the area, the effects will be cumulative and the inundation and destruction even greater.The historic record shows that there have been many tsunamis that have struck the shores with devastating force, sometimes reaching heights of more than 30-50 meters. For example, the 1946 tsunami generated by an earthquake off Unimak island in Alaska's Aleutian Islands, reached heights of more than 35 meters, which destroyed a reinforced concrete lighthouse and killed its occupants.

Finally, the maximum height a tsunami reaches on shore is called the runup. It is the vertical distance between the maximum height reached by the water on shore and the mean sea level surface. Any tsunami runup over a meter is dangerous. The flooding by individual waves will typically last from ten minutes to a half-hour, so the danger period can last for hours. Tsunami runup at the point of impact will depend on how the energy is focused, the travel path of the tsunami waves, the coastal configuration, and the offshore topography. Small islands with steep slopes usually experience little runup  wave heights there are only slightly greater than on the open ocean. This is the reason that islands with steep-sided fringing or barrier reefs are only at moderate risk from tsunamis. However, this is not the case for islands such as the Hawaiian or the Marquesas. Both of these island chains do not have extensive barrier reefs and have broad bays exposed to the open ocean. For example, Hilo Bay at the island of Hawaii and Tahauku Bay at Hiva Oa in the Marquesas are especially vulnerable. The 1946 Aleutian tsunami resulted in runup, which exceeded 8 m at Hilo and 10 m at Tahauku; 59 people were killed in Hilo and two in Tahauku. Similarly, any gap in a reef puts the adjacent shoreline at risk. The local tsunami from the Suva earthquake of 1953 did little damage because of Fiji's extensive offshore reefs. However, two villages on the island of Viti Levu, located on opposite gaps in the reef, were extensively damaged and five people were drowned.Back to Top

11. What are some of the largest historical tsunamis?

Destructive tsunamis have occurred in all of the world's oceans and seas. In the last half of the 20th Century, Pacific-wide, destructive tsunamis occurred in 1946, 1952, 1957, 1960, and 1964. (Many more tsunamis in inland seas around the periphery of the Pacific, where extremely destructive locally and claimed thousands of lives. Such localized tsunamis occurred in 1975, 1983, 1985, 1992, 1993, 1995, 1998, 1999 and 2001.

The 1 April 1946 Aleutian Earthquake and TsunamiOne of the most destructive Pacific-wide tsunamis was generated by a magnitude 7.8 earthquake near Unimak Island in Alaska's Aleutian Island Chain. A huge wave of 35 meters destroyed completely the U.S. Coast Guard's Scotch Cap lighthouse on Unimak and killed all five of its occupants. The lighthouse was a steel-reinforced concrete structure standing about 30 meters above sea level. Without warning, destructive tsunami waves reached the Hawaiian Islands, five hours later, causing considerable damage and loss of life. The waves completely obliterated Hilo's waterfront on the island of Hawaii, killing 159 people there. Altogether a total 165 people lost their lives from this tsunami, including children attending school at Hawaii's Laupahoehoe Point, where waves reaching up to 8 m destroyed also a hospital. Damage was estimated at $26 million (in 1946 dollars). In 1948, and as a result of this tsunami, the U.S. established a Pacific Tsunami Warning Center in Hawaii.Back to Top

The 4 November 1952 Kamchatka Earthquake and TsunamiA strong earthquake (magnitude 8.2) off the coast of Kamchatka Peninsula generated a great destructive Pacific-wide tsunami. Its waves struck the Kamchatka Peninsula, the Kuril Islands and other areas of Russia's Far East, causing considerable damage and loss of life. The tsunami was widely observed and recorded in Japan, but there was no loss of life or damage there. There was considerable damage in the Hawaiian Islands and some damage in Peru and Chile. The tsunami was recorded or observed throughout the islands of the Pacific. In New Zealand waves reached height of 1m. In Alaska, in the Aleutian Islands and in California waves of up to 1.4 meters were observed or recorded.

By far the largest waves outside the generating area were observed in the Hawaiian Islands. Fortunately, no human lives were lost in Hawaii from this tsunami, but damage was extensive, estimates ranging from $800,000- $1,000,000 (in 1952 dollars). The tsunami caused damage on Midway Island. Elsewhere in the Hawaiian island chain, the waves destroyed boats and piers, knocked down telephone lines, and caused extensive beach erosion. In some locations, tsunami waves were destructive in certain locations but hardly noticeable at others. The north shore of the Island of Oahu experienced higher waves of up to 4.5 meters. On the south shore of the island, the tsunami was powerful enough to throw a cement barge in the Honolulu Harbor into a freighter. The island of Hawaii experienced run up to 6.1 meters. In Hilo, a small bridge connecting Coconut Island to the shore was destroyed by one of the tsunami waves lifting it off its foundation, then smashing it down. The effects of the tsunami in the generating area in Kamchatka, varied significantly. From Kamchatka Peninsula to Kronotsky Peninsula the wave heights ranged from zero to 5 meters. From Kronotsky Peninsula to Cape Shipursky the heights ranged from 4-13 meters. The highest wave of 13 meters was the third and was observed at Olga Bay, where it caused considerable damage. Travel time of the first tsunami wave to Olga Bay was approximately 42 minutes after the earthquake. From Cape Shipursky to Cape Povorotny, the tsunami waves ranged from 1 to 10 meters and caused considerable loss of life and damage. At Avachinskaia Bay the tsunami height was 1.2 meters and its travel time was about 30 minutes. From Cape Povorotny to Cape Lopatkka the waves ranged from 5 to 15 meters. At Khodutka Bay a cutter was thrown 500 meters back from shore. On the West coast of Kamchatka Peninsula, the maximum tsunami runup at Ozernoe was 5 meters. At Alaid Island of the Kuril Island group, run up was 1.5 meters. At Shumshu Island it ranged from 7-9 meters. At Paramushir Island the waves ranged from 4-18.4 meters. At Severo  Kurilsk on Paramushir Island, the second wave was the highest reaching maximum run up of 15 meters. It destroyed most of the town and caused considerable loss of life. At Onekotan Island tsunami run up was 9 meters, while at Shiashkoton Island it was 8 meters and at Iturup Island 2.5 meters. Waves of up to 2 meters were observed at the Komandorsk Islands and at Okhotsk. At Sakhalin  Korsakov a 1-meter tsunami wave was observed.Back to Top

The 9 March 1957 Aleutian Earthquake and TsunamiOn March 9, 1957, an 8.3 magnitude earthquake south of the Andreanof Islands, in the Aleutian Islands of Alaska  in the same general area as that of April 1, 1946  generated a Pacific-wide tsunami. Although no lives were lost, there was extensive destruction of property in the Hawaiian Islands, with damage estimated at approximately $5 million (1957 dollars). The waves were particularly high on the north shore of the island of Kauai where they reached a maximum height of 16 meters, flooding the highway and destroying houses and bridges. This was twice the height of the 1946 tsunami. At Hilo, Hawaii, the tsunami runup reached 3.9 m and there was damage to numerous buildings along the waterfront. Within Hilo Bay, Coconut Island was covered by 1 m of water and the bridge connecting it to the shore, as in 1952, was again destroyed.Back to Top

The 22 May 1960 Chilean Earthquake and TsunamiThe largest earthquake (magnitude 9.5) of the 20th century occurred on May 22, 1960 off the coast of south central Chile. It generated a Pacific-wide tsunami, which was destructive locally in Chile and throughout the Pacific Ocean. The tsunami killed an estimated 2,300 people in Chile. There was tremendous loss of life and property in the Hawaiian Islands, in Japan and elsewhere in the Pacific. Destructive waves in Hilo, Hawaii, destroyed the waterfront and killed 61 people. Total damage was estimated at more than $500 million (1960 dollars).Back to Top

The 27-28 March 1964 Alaska Earthquake and TsunamiThe largest earthquake of the 20th Century in the northern hemisphere, with a magnitude 8.4, affected an area in Alaska that was almost 1600 km long and more than 300 km wide  extending from Valdez to the Trinity Islands, southwest of Kodiak Island in the Gulf of Alaska. The earthquake caused areas to be lifted by as much as 15 m (50 feet) in certain areas, while many other areas subsided greatly. In addition to many local tsunamis generated within the Prince William Sound, vertical crustal displacements averaging 1.8 m (6 ft.) over an area of about 300,000 square kilometers (115,000 square miles) extending in the Gulf of Alaska's continental shelf, generated a Pacific-wide tsunami. Its waves were very destructive in southeastern Alaska, in Vancouver Island (British Columbia), and in the U.S. States of Washington, California and Hawaii. The tsunami killed more than 120 people and caused more than $106 million in damages, making it the costliest ever to strike the Western United States and Canada. Five of Alaska's seven largest communities were devastated by the combination of earthquake and tsunami wave damage. Alaska's fishing industry and most seaport facilities were virtually destroyed. Tsunami waves at Kodiak Island washed away a total of 158 houses and buildings within two blocks of the waterfront. Fishing boats were carried hundreds of meters inland. The 1964 tsunami waves caused also extensive damage in Vancouver Island (British Columbia), and in the states of Washington, California and Hawaii, in the United States. The waves affected the entire California coastline, but were particularly high from Crescent City to Monterey ranging from 2.1 - 6.3 meters (7-21 feet). Hardest hit was Crescent City, California, where waves reaching as much as 6 meters (20-21 feet) destroyed half of the waterfront business district. Eleven persons lost their lives there. At Santa Cruz Harbor, the tsunami waves reached as high as 3.3 meters (11 feet) causing some damage. There was extensive damage in San Francisco Bay, the marinas in Marin County and at the Noyo, Los Angeles and Long Beach harbors. Estimated losses in California were between $1,500,000 and $2,375,000 (1964 dollars), while at Crescent City tsunami damage was estimated at $7,414,000.Back to Top

12. Why are locally generated tsunamis so dangerous?

A locally generated tsunami may reach a nearby shore in less than ten minutes. There is not sufficient time for the Pacific Tsunami Warning Center or for local authorities to issue a warning. For people living near the coast, the shaking of the ground is a warning that a tsunami may be imminent. For tsunamis from more distant sources, however, accurate warnings of when a tsunami might arrive are possible because tsunamis travel at a known speed.Back to Top

If you feel a large earthquake, should you wait for a warning or evacuate?

How are tsunami generated?

Do all large earthquakes, greater than magnitude 7.0 generate dangerous tsunamis?

What was the biggest earthquake ever recorded?

Does Alaska have a history as a dangerous tsunami source region?

What does the word 'tsunami' mean?

Can a tsunami sink a ship?

TsuInfo Alert NewsletterAnd in case your question falls within the range of "Infrequently" Asked Questions, try looking at the online issues of TsuInfo Alert Newsletter. Each issue usually has a column of questions compiled by Lee Walkling of Washington's Division of Geology and Earth Resources Library. Example question: If you hiked Mt. St. Helens, could you find evidence of a tsunami?Back to Top

14. What is a mega-tsunami and can it happen today?

The following is a position paper that was issued by the Tsunami Society concerning the occurrence of Mega-Tsunamis:

The mission of the Tsunami Society includes "the dissemination of knowledge about tsunamis to scientists, officials, and the public". We have established a committee of private, university, and government scientists to accomplish part of this goal by correcting misleading or invalid information released to public about this hazard. We can supply both valid, correct and important information and advice to the public, and the names of reputable scientists active in the field of tsunami, who can provide such information.

Most recently, the Discovery Channel has replayed a program alleging potential destruction of coastal areas of the Atlantic by tsunami waves which might be generated in the near future by a volcanic collapse in the Canary Islands. Other reports have involved a smaller but similar catastrophe from Kilauea volcano on the island of Hawaii. They like to call these occurences "mega tsunamis". We would like to halt the scaremongering from these unfounded reports. We wish to provide the media with factual information so that the public can be properly informed about actual hazards of tsunamis and their mitigation.

Here are a set of facts, agreed on by committee members, about the claims in these reports:

While the active volcano of Cumbre Vieja on Las Palma is expected to erupt again, it will not send a large part of the island into the ocean, though small landslides may occur. The Discovery program does not bring out in the interviews that such volcanic collapses are extremely rare events, separated in geologic time by thousands or even millions of years.

No such event  a mega tsunami  has occurred in either the Atlantic or Pacific oceans in recorded history. NONE.

The colossal collapses of Krakatau or Santorin (the two most similar known happenings) generated catastrophic waves in the immediate area but hazardous waves did not propagate to distant shores. Carefully performed numerical and experimental model experiments on such events and of the postulated Las Palma event verify that the relatively short waves from these small, though intense, occurrences do not travel as do tsunami waves from a major earthquake.

The U.S. volcano observatory, situated on Kilauea, near the current eruption, states that there is no likelihood of that part of the island breaking off into the ocean.

These considerations have been published in journals and discussed at conferences sponsored by the Tsunami Society.

Some papers on this subject include:

"Evaluation of the threat of Mega Tsunami Generation From ....Volcanoes on La Palma ... and Hawaii", George Pararas-Carayannis, in Science of Tsunami Hazards, Vol 20, No.5, pages 251-277, 2002.